Hey there , after looking at your logs all i can say is that you are doing more than fine. Chain heal is doing more than 5 bounces on average which is rly good, elemental blast is being used fine as well.
Reason why your healing is low is mostly cuz you are running heavy healing setup ( 2 paladins and disc on most of fights ).
Things that you can improve: Your major cds are doing low amount of healing , for example on council on 6 min fight you used healing tide only once and it did only 2.4mil healing which is rly low.
You can try running with AS instead of echo so you can snipe heals bit better with more haste but overall really you are doing well considering amount of healers you are using.
So my advice for you is to keep executing fights correctly,do whatever is raid leader asking from you and dont worry that much about numbers while you are heavy healing fights. If you ever reduce amount of healers and you still have issues with numbers feel free to update us with fresh logs 😀